Condensation polymers such as thermoplastic polyesters, polycarbonates, and polyamides have many desirable physical and chemical attributes that make them useful for a wide variety of molded, fiber, and film applications. However, for specific applications, these polymers also exhibit limitations that should be minimized or eliminated. To overcome these limitations, polymers are frequently made containing one or more additives or comonomers depending upon the desired end use of the polymer. One of the most common thermoplastic polyester polymers is polyethylene terephthalate (PET).
PET polymer is used extensively in the packaging industry, especially in the production of bottles for carbonated and non-carbonated beverages. In the carbonated beverage industry, concerns include the rate of carbon dioxide escape from the container, taste deterioration of the contents due to degradation by light, and extraction of additives added either during melt polymerization or subsequent melt processing that is required to fabricate the container. To overcome these problems, PET resins are often modified by incorporating unique comonomers into the polymer backbone thus producing a wide variety of PET copolyesters. For example, 2,6-naphthalenedicarboxylate (2,6-NDC) is copolymerized with ethylene glycol (EG) and terephthalic acid (TPA), propylene glycol is copolymerized with ethylene glycol (EG) and terephthalic acid (TPA) (U.S. Pat. No. 6,313,235), and isophthalic acid (IPA) is copolymerized with ethylene glycol (EG) and terephthalic acid (TPA) (U.S. Pat. Nos. 7,297,721, 6,489,434, and 6,913,806).
Condensation polymers may be degraded by hydrolysis with catalyst of acid, or base. The rate of depolymerization depends upon the structure of the polymers. Poly(hydroxyl acids), such as poly glycolic acid or poly lactic acid or copolymers of glycolic acid and lactic acid are easily hydrolyzed at mild conditions, even at pH 7 and room temperature in several months. Therefore, poly(hydroxyl acids) have wide applications based on their degradability, such as in medical devices and drug delivery system. On the other hand, polyethylene terephthalate (PET) hydrolyzes very slowly at mild conditions. To decompose such kind of polyester will require high temperature and high pressure through reaction with methanol, ethylene glycol or ammonia/glycol, which all involves organic solvents. PET and its derivatives have also wide applications based on their non-degradability and mechanical strength, such as fibers, packaging bottles and films.
Although there are many attempts to modify condensation polymers for extension of their application as described above, no attempts have been reported to incorporate degradable blocks of polyester into non-degradable condensation polyester in which the degradable blocks are uniformly distributed in the polymer chains.